This invention relates to the field of air cleaning, and particularly to a new air cleaner for precleaning use with agricultural machinery which must operate in an environment of airborne chaff.
In such environments the life of an air filter if used alone is impractically short, and the practice has arisen of installing a centrifugal cleaner in the line conducting ambient air to the filter, to remove the larger particles which otherwise quickly clog the filter. In such installations the centrifugal cleaner is known, from its spatial location, as a precleaner. By its use the service life of a subsequent air filter is greatly extended, and by scavenging the centrifugal precleaner a very acceptable overall system results.
We are aware that it is known to mount a centrifugal precleaner having a closed top with its axis vertical, ambient air being drawn in through spiral louvers around the upper portion of the device, and treated air being drawn out through a reentrant axial outlet conduit in the otherwise closed bottom, and a tangential scavenger opening being provided in the lower portion for connection to a suitable aspirator to continuously dispose of centrifugally separated particulate matter. The principal flow of air through the cleaner is helically downward, and a parasitic eddy of air is present at the top of the cleaner.
This arrangement has several advantages, but suffers from an imperfection in operation, particularly where the air ambient to the device is laden with pollutants of low density such as particles of chaff. We have found that a considerable part of this material is deflected upwardly into the eddy just mentioned, during precleaner operation, to form a continuously rotating central mass at the top of the precleaner: when the flow of air is terminated, as by shutting down an engine being supplied therewith, the eddy disintegrates and the circling mass of chaff simply drops down into the outlet conduit, to be ingested when the air flow is next resumed: this of course is undesirable.